This invention relates to a DC power supply and more particularly to a power supply that may be economically employed as a supply for the electronic controls in an electrical appliance.
The power supply of the present invention was conceived to provide power for the control circuits employed in a microwave oven. Mirowave ovens now provide the user with increasingly sophisticated electronic controls, including touch panel digital controls. These electronic controls often require both a low DC voltage and a higher DC voltage, for example about 15 volts and about 60 volts. Conventionally, these DC levels are obtained by providing a transformer having a secondary winding for each of the voltages, or by providing two transformers. In this case, one winding would present an AC voltage with a peak value somewhat in excess of the desired 60 volts to a recitifying and smoothing network to generate 60 volts DC, while another transformer winding and rectifying circuit provides the desired lower voltage. (i.e. 15 volts).
The power supply of the present invention can be connected to the 24 volts RMS center tapped overwinding on a cooling fan motor coil of the microwave oven to derive both the desired high and low voltages required. This results in economy as well as savings of space, since it overcomes the requirement for a transformer having two secondary windings or two separate transformers. Of course, although the invention is described in conjunction with the use in a microwave oven, it can also be used to advantage with any transformer having a single, center tapped, secondary winding, where two voltages having the relationship described are required, at a savings of one rectifier over the existing art.